The present invention relates to diaphragms for use in loud speakers, and more particularly, to diaphragms of the dome-shaped type.
Conventionally, aluminum or titanium were used for the most part as the material of a diaphragm because of their lightness in weight and their facility in rolling treatment. Those materials, however, produce a particular vibrating mode over the diaphragm so that in the high-frequency characteristic of the diaphragm, there appears a peak portion thereby causing the reproduced tone qualities to be considerably degraded. For the purpose of avoiding the disadvantage encountered, it has been recognized that a material having a large ratio of Young's modulus E to density .rho. is preferable therefor in order to obtain a highly efficient diaphragm (See Table 1). Because of this recognition beryllium, or beryllium alloy has been used as the material for diaphragms.
Beryllium or beryllium alloy are similar to aluminum in that the surfaces thereof are not corroded due to the formation of oxidizing films thereon. However, the surfaces thereof can be corroded by certain environments, such as in sulfurous acid gas, and may suffer from the recent terrific air pollution which includes corrosive gasses, such as sulfurous acid gas, caused mainly by the exhaust gas from automobiles and the exhaust smoke from industries.
Table 1 ______________________________________ Young's modulus Density .rho. E/.rho. Kg/mm.sup.2 g/cc 10.sup.-6 cc/mm.sup.2 ______________________________________ Aluminum 7,400 2.65 2,750 Boron carbide 46,000 2.51 18,326 Beryllim 28,000 1.84 15,217 Boron 45,000 2.46 18,292 ______________________________________